The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Since eco-friendly vehicles such as hybrid vehicles and electric vehicles are driven based on electric energy, motor driven air compressors, which are different from conventional mechanical air compressors operating to be interlocked with an engine, are installed on eco-friendly vehicles.
FIG. 1 is a diagram illustrating an existing, conventional motor driven air compressor management system applied to an electric vehicle, and FIG. 2 is a flowchart illustrating an operation of the existing motor driven air compressor management system.
Generally, a motor driven air compressor 10 generates compressed air which is used in an air brake system of a commercial vehicle, and the generated compressed air is stored in an air tank 40 via a separator cooler 20 and an air dryer 30.
To this end, the motor driven air compressor 10 operates by receiving power of a power through an inverter 12.
That is, when a starting of a vehicle is turned on, a controller 11 of the vehicle applies the power of the battery to the inverter 12, and the inverter 12 performs voltage control on the motor driven air compressor 10 such that an operation of the motor driven air compressor 10 is performed.
Accordingly, the compressed air generated by the operation of the motor driven air compressor 10 fills to be stored in the air tank 40 via the separator cooler 20 and the air dryer 30, and the stored compressed air is used when an air brake is operated.
At this point, the separator cooler 20 primarily removes foreign materials of the compressed air generated in the motor driven air compressor 10 (e.g., an oil component and water which are vaporized as a hydraulic fluid of the motor driven air compressor 10) in a centrifugal separation manner, and simultaneously, the separator cooler 20 serves to cool the generated compressed air because the generated compressed air generated in the motor driven air compressor 10 is in a high temperature state.
Further, the air dryer 30 serves to secondarily remove foreign materials (residual oil, moisture, and the like) of the compressed air flowing from the separator cooler 20 in an absorption manner.
Meanwhile, a double check valve 22 is installed at an exhaust port valve 21 of the separator cooler 20, and a control line 46 to which a maximum filling pressure of the compressed air acts through a purge pot 31 of the air dryer 30 is connected between the purge pot 31 of the air dryer 30 and a first inlet 22-1 of the double check valve 22.
Further, a pneumatic switch 32 which is turned on in an off-load condition of the motor driven air compressor 10 is installed at a control line 46, and an air backflow line 44 at which a solenoid valve 42 is installed is connected between a second inlet 22-2 of the double check valve 22 and the air tank 40.
FIG. 3 is a graph showing a pressure variation of the air tank 40 of the conventional system.
As shown in FIG. 3, the motor driven air compressor 10 repeats an on-load operation (ON) and off-load operation (OFF) according to set pressures P1 and P2 of the air dryer 30, and in {circle around (1)} section which is an on-load section of the motor driven air compressor 10, a pressure of the air tank 40 is increased by filling the compressed air in the air tank 40, whereas in a {circle around (2)} section which is an off-load section of the motor driven air compressor 10, the a pressure of the air tank 40 is decreased.
In this case, when the compressed air filling in the air tank 40 reaches a maximum filling pressure, the compressed air pressure acting on the control line 46 through the purge pot 31 of the air dryer 30 is referred to as a control line pressure P, and a pressure capable of performing an on-operation by the control line pressure P acting on the control line 46 is referred to as a pneumatic switch operating pressure Pset.
In an operation condition of the motor driven air compressor 10 (control line pressure P<pneumatic switch operating pressure Pset), the compressed air generated by an operation of the motor driven air compressor 10 fills in the air tank 40 via the separator cooler 20 and the air dryer 30.
Meanwhile, in an off-load condition of the motor-driven air compressor 10 (control line pressure P>pneumatic switch operating pressure Pset), the pneumatic switch 32 is turned on by a pressure of the control line 46 and, simultaneously, an on-operation signal is transmitted to the inverter 12, the inverter 12 receiving the on-operation signal of the pneumatic switch 32 interrupts an operation of the motor driven air compressor 10, and the control line pressure P acting on the control line 46 passes through the first inlet 22-1 of the double check valve 22 and is exhausted to the outside through the exhaust port valve 21 of the separator cooler 20.
In this case, when the control line pressure P does not act, the exhaust port valve 21 of the separator cooler 20 is closed, and when the control line pressure P acts, the exhaust port valve 21 is opened to communicate with the atmosphere.
Thus, after the control line pressure P passes through the first inlet 22-1 of the double check valve 22 while turning the pneumatic switch 32 on, the control line pressure P acts on the exhaust port valve 21 such that the exhaust port valve 21 is opened and the control line pressure P is exhausted to the outside.
Further, in the off-load condition of the motor-driven air compressor 10, the controller 11 controls the solenoid valve 42, which is installed at the air backflow line 44 to be selectively opened.
Accordingly, some portion of the compressed air filling in the air tank 40 passes through the solenoid valve 42 of the air backflow line 44, passes through the second inlet 22-2 of the double check valve 22, and then is exhausted to the outside through the exhaust port valve 21 of the separator cooler 20, and at this point, some portion of the compressed air from the air tank 40 acts on the exhaust port valve 21 and the exhaust port valve 21 is opened by a pressure of the compressed air such that foreign materials (e.g., an oil component vaporized as a hydraulic fluid of the motor-driven air compressor 10, moisture, and the like) may be discharged and removed by some portion of the compressed air exhausted through the exhaust port valve 21.
Meanwhile, as described above, while the motor driven air compressor 10 operates in the operating condition of the motor driven air compressor 10 (the control line pressure P<pneumatic switch operating pressure Pset) and the compressed air fills in the air tank 40, there may occur a case in which a starting of the vehicle is factitiously turned off such that the motor driven air compressor 10 is turned off, or the motor driven air compressor 10 is turned off by a cause of an abnormal operation (e.g., overheating of a motor of the motor driven air compressor 10, and the like).
When the motor driven air compressor 10 is turned off during driving, a residual pressures is present in the air filling line 13 connected between the motor driven air compressor 10 and the separator cooler 20, and in the air filling line 14 connected between the separator cooler 20 and the air dryer 30.
Thereafter, when the motor driven air compressor 10 operates again, an electrical load on the motor of the motor driven air compressor 10 by the residual pressure which is present in the air filling lines 13 and 14 may cause the motor driven air compressor 10 to not operate.
As described above, when a pressure of air, which fills in the air tank 40 by an operation of the motor driven air compressor 10, reaches a maximum pressure, a pressure is generated in the control line 46. At this point, when the control line pressure P acting on the control line 46 is equal to or greater than the pneumatic switch operating pressure Pset, the pneumatic switch 32 is turned on.
Subsequently, the pneumatic switch 32 is turned on and, simultaneously, the on-operation signal is transmitted to the inverter 12, the inverter 12 receiving the on-operation signal for the pneumatic switch 32 interrupt the operation of the motor driven air compressor 10, and the control line pressure P acting on the control line 46 passes through the first inlet 22-1 of the double check valve 22 and is exhausted to the outside through the exhaust port valve 21 of the separator cooler 20.
As described above, together with the interruption of an operation of the motor of the motor driven air compressor 10, the control line pressure P applied to the control line 46 is exhausted through the exhaust port valve 21 of the separator cooler 20, i.e., a so-called residual pressure removal is performed, but when the control line pressure P is less than the pneumatic switch operating pressure Pset, a residual pressure remains in the air filling lines 13 and 14.
A phenomenon we have discovered in which the residual pressure remains in the air filling lines 13 and 14 will be described in detail below with reference to FIG. 4.
FIG. 4 illustrates ON and OFF periods of the pneumatic switch 32 of the conventional system, ON and OFF periods of the motor of the motor driven air compressor 10, and pressure variations of the air tank 40 and the control line 46.
While the motor driven air compressor 10 operates and compressed air fills in the air tank 40 as described above, when there occurs a situation in which the motor driven air compressor 10 is turned off manually or the motor driven air compressor 10 is turned off due to an abnormal operation cause (e.g., overheating of the motor of the motor driven air compressor 10), as indicated by a bold line and an initial control line pressure Pi in FIG. 4, a pressure acting on the control line 46 does not rise to the control line pressure P which is a maximum pressure capable of turning the pneumatic switch 32 on and rises to a certain level to finally drop such that a residual pressure of the compressed air corresponding to the initial control line pressure Pi remains in the air filling lines 13 and 14.
As described above, while the motor driven air compressor 10 operates and the compressed air fills in the air tank 40, when there occurs a situation in which the motor driven air compressor 10 is turned off manually or due to an abnormal operation cause, the residual pressure of the compressed air remains directly in the air filling line 13 connected between the motor driven air compressor 10 and the separator cooler 20, and in the air filling line 14 connected between the separator cooler 20 and the air dryer 30.
Thus, when a starting of the motor driven air compressor 10 is turned on again in a state in which the residual pressure remains in the air filling lines 13 and 14, an electric load is increased to the motor of the motor driven air compressor 10 due to the residual pressure such that there may be a situation in which an initial operation of the motor driven air compressor 10 is not smoothly performed.
The above information disclosed in this Background section is only for enhancement of understanding of the background and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.